1. Field of the Invention
The present invention relates to improvements in a method of manufacturing poly-V pulleys and such products, and more particularly to improvements in a method of manufacturing poly-V pulleys with the use of a step of thickening the pulley peripheral wall.
2. Prior Art
In recent years sheet metal poly-V pulleys have been widely used, each of which is made in such a way that a metal plate is subjected to drawing to produce a cup-shape blank, and then a plurality of annular sharp V-grooves called poly-V grooves are formed in the peripheral wall of such cup-shape blank. As compared with pulleys made with the use of a widely known mold, such sheet metal poly-V pulleys present advantages in that they are of lighter weight and manufactured with reduced costs. Therefore, such poly-V pulleys have been widely used in the automobile industry or the like.
As far as is known, there are two types of sheet metal poly-V pulleys and methods of manufacturing the same.
According to a first type, the cylindrical peripheral wall of a cup-shape blank is compressingly folded to produce V-shape grooves, so that a completed product poly-V pulley is obtained.
According to a second type, as disclosed in U.S. Pat. No. 4,273,547, a so-called peripheral wall thickening step is used; namely, the cylindrical peripheral wall of a cup-shape blank is thickened before being subjected to rolling with the use of a V-shape groove-forming roller.
The present invention relates to improvements in the invention of the second type mentioned above.
U.S. Pat. No. 4,273,547 discloses a poly-V pulley made in such a way that a metal plate is subjected to drawing to produce a cup-shape blank, the cylindrical peripheral wall of the cup-shape blank is then thickened, and a so-called rolling is performed with a V-shape groove-forming roller pressingly applied to the outer surface of the thickened cylindrical peripheral wall, thereby forming a plurality of parallel V-shape annular grooves in this outer surface, running in the peripheral direction of the cylindrical peripheral wall.
As the result, today it is possible to manufacture practical poly-V pulley having a sufficient mechanical strength even though made with a thin metal plate processed with low manufacturing costs. However, it was nevertheless desirable to develop a more economical poly-V pulley of lighter weight.